In a context of compressed image data transmission in which the available bit rate and the disturbances affecting the channel are variable, it is necessary to be able to adapt, at any time, the useful bit rate of a compressed data stream and its resistance to errors in order to adapt to the variations of the constraints due to the environment. To this end, it is therefore important to be able to estimate the characteristics of a compressed image stream such as the bit rate and the compression distortion, after the compression step and without decoding said stream. Another important characteristic to be estimated is the distortion of the decoded image resulting from the loss or from the corruption during its transmission of a packet contained in the compressed stream. This information makes it possible to measure the influence on the visual rendering of the propagation errors which affect the transmission channel and to deduce therefrom, notably, an appropriate strategy for protecting the compressed stream by adding redundancy.
The problem in estimating the bit rate and distortion of a compressed image stream is notably dealt with in the context of the bit rate/distortion allocation which aims to determine the best quantization parameters to be applied by an image compression mechanism in order to obtain a distortion on the decoded image that is as low as possible for a given bit rate. The document [1] proposes a number of bit rate and/or distortion allocation models for the coding of images and of videos, but it does not deal with the problem of estimating the distortion on image streams that are already compressed and with no prior knowledge of the encoded image.
There are methods for modeling the sensitivity to errors of a video stream such as that disclosed in the French patent [2], but the latter is limited to the case of application to the H.264 video standard. The method implemented in this patent presupposes, in addition, an interaction with the source coder and/or the knowledge, from the point of view of the receiver, of the original video sequence transmitted.